schedule.go

package main

import (
	"fmt"
	"math/rand"
	"os"
	"os/signal"
	"syscall"
	"time"
)

// schedule function calls the `fn` function after `freq` time of it's last
// call
func schedule(fn func(), freq time.Duration, stopChan chan struct{}) {
	for {
		select {
		case <-time.After(freq):
			fn()
		case <-stopChan:
			fmt.Println("stop")
			stopChan <- struct{}{}
			return
		}
	}
}

// task is a dummy example for a task
// sometimes it will take more than me.Duration to finish the task
func task(name string, t time.Duration) func() {
	lastCall := time.Now()
	return func() {
		s := rand.Intn(int(t) + 500)
		time.Sleep(time.Duration(s) / 1000000 * time.Millisecond)
		now := time.Now()
		fmt.Println("task", name, s, now.Sub(lastCall))
		lastCall = now
	}
}

func main() {
	termChan := make(chan os.Signal)
	signal.Notify(termChan, syscall.SIGTERM, syscall.SIGINT)

	stopChan := make(chan struct{})
	go func() {
		callFreq := time.Second
		schedule(task("A task", callFreq), callFreq, stopChan)
	}()

	<-termChan

	// we use the stopChan channel to notify the scheduler that it should stop executing tasks
	stopChan <- struct{}{}
	// we also use the stopChan channel to get notified that the scheduler stopped
	<-stopChan

}